It is known that in order to make foundations for buildings it is necessary to make concrete piles, for which bore holes must be made in the ground.
In order to make said piles, known in the art are devices based on the utilization of continuous-screw augers provided with means for injecting the concrete into the hole. The drilling operation is thus combined with that of filling the hole with concrete up to the desired height.
The auger can be driven by a conventional drilling crane.
This type of foundation device is especially useful in sites with a certain degree of compaction. Where the ground is soft, however, the walls of the hole which it forms are not compact, and this can further lead to high consumption of concrete, because it penetrates deeper into the ground.
The conventional devices for drilling and compacting have the disadvantage that they require high driving power and, therefore, large and costly machines, since the shaft of the auger is practically of the same diameter as the pile to be made. Moreover, in the case of very soft soils, in order to improve their quality recourse is frequently had to strengthening the soil by injection of compacting products which are mixed with the soil, forming an emulsion-like paste, using devices which drive two or more augers in opposite directions.
Other technical solutions have also been provided to improve the quality of the hole, for example using a continuous-screw auger to combine the drilling operation with that of rendering the wall of the hole by injecting concrete against said wall, thereby providing it with a coating layer. A concrete jacket is thus achieved which provides the hole with suitable uniformity.
In this case also, there is the disadvantage of excessive consumption of concrete, so that for soft soils recourse is usually had to extracting the auger at higher speed, at the same time as the latter injects the concrete, thereby reducing the consumption. This operation can nevertheless lead to the wall of the hole having weak points at the strata of the ground where the soil is less compact.
The soil is sometimes drilled and then lined using formwork pipes which are sunk into the drilled bore hole. This lining operation can be carried out simultaneously with drilling, in such a way that the auger passes through the interior of the tube. However, this is a costly operation owing to utilization of such tubes, and it is also complicated due to extraction of the tube after the hole has been filled with concrete.
As can be seen, there exist a plurality of devices providing different solutions for making holes for foundation piles.
U.S. Pat. No. 3,604,214 discloses a method which comprises forming a bore by making two augers rotation in a synchronized fashion. Then the augers are raised out from the formed bore while fluid material is fed into the bore. For this operation, a smaller of the two augers is rammed downwardly to the lower end of the passage. The feeding of material is preformed by rotating the smaller auger within the larger of the two augers to thereby force the material into to the bore
U.S. Pat. No. 4,504,173 discloses an apparatus and method of constructing tubular piles, the apparatus comprising two coaxially mounted tools for forming holes and the method comprises driving the apparatus into the soil to form the hole and then withdrawing it while simultaneously filing the hole with concrete material.
Finally, U.S. Pat. No. 4,595,059 discloses a method for providing a conductor pipe to an opening portion of a well. The method comprises forming a bore in the ground by means of a casing tube provided with an external round steel segment spirally welded about an outer surface of the casing tube and an inner auger screw. The tube and auger rotate in mutually opposite directions while advancing together (flush) into the ground. Subsequently, the inner auger is withdrawn leaving the outer tube in the ground as a casing.